Apparatus using reflected polarized light to inspect a moving web

ABSTRACT

In an inspection system for detecting defects in the photosensitive surface of photographic material, laser means grazes visible light off the photosensitive surfaces of photographic material. The light is swept rapidly across the surface of the photosensitive material; and such light is polarized so that its plane of polarization is perpendicular to its plane of incidence. The special polarization, together with the rapid sweeping of the light across the photosensitive surface, prevents the photosensitive surface from producing latent images.

Unite States Patent 1 1 Cornelius [4 1 May 22, 1973 s41 APPARATUS USHJGREFLECTED 3,515,488 6/1970 l-louser ..356/200 POLARIZED LIGHT o INSPECTA 3,612,692 10/1971 Druppe ..356/1 14 MOVING WEB Edward C. Cornelius,Fairport, N.Y.

Eastman Kodak Rochester, N.Y.

Filed: May 6, 1971 Appl. No.: 140,932

Inventor:

Assignee: Company,

U.S. Cl ..356/ll8, 356/200 Int. Cl. ..G03b 27/04 Field of Search..356/209, 211, 118, 356/ll4, 116,200, 237

References Cited UNITED STATES PATENTS 3/1964 Warren et al ..356/200Primary Examiner-Edward S. Bauer Attorney-W. T. French, R. F. Crockerand Robert F. Cody [57] ABSTRACT In an inspection system for detectingdefects in the photosensitive surface of photographic material, lasermeans grazes visible light off the photosensitive surfaces ofphotographic material. The light is swept rapidly across the surface ofthe photosensitive material; and such light is polarized so that itsplane of polarization is perpendicular to its plane of incidence. Thespecial polarization, together with the rapid sweeping of the lightacross the photosensitive surface, prevents the photosensitive surfacefrom producing latent images.

6 Claims, 3 Drawing Figures PATENIEL Elf-ff 2 2 I973 EDWARD C COR/VENUSINVENTOR.

ATTORNEY APPARATUS USING REFLECTED POLARIZED LIGHT TO INSPECT A MOVINGWEB BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to the inspection of photographic materials; and in particularto the inspection of the surfaces of photographic webs.

2. Description Relative to the Prior Art The detectionof surface defectsin the emulsion coat on a photographic web, by grazing a beam ofinfrared radiation off the surface of the web, is well known. See U.S.Pat. No. 3,125,265. A frequent problem with such technique, however, isthat part of the beam may penetrate the emulsion and be reflected offthe base support for the emulsion, thereby sometimes providing anambiguity to which a photopickup, responsive to the reflected infraredradiation, would undesirably respond.

It has been demonstrated that, by use of reciprocity law failure,visible light may be employed to inspect unexposed photographicemulsions. See U.S. Pat. No. 3,556,664. Use of visible light, as opposedto the prior art use of infrared radiation, in a reflection inspectionsystem, would have several advantages, least of which is that visiblelight can be seen, and alignment of the inspection apparatus would,therefore, be greatly simplified. Also, photopickups that are responsiveto visible light have SignaLto-noise qualities which are several ordersbetter than those which are responsive to infrared radiation; andshorter wavelength (i.e., visible) light is inherently more easilydefined into a very small spot for purposes of detecting and resolvingextremely small surface defects.

SUMMARY OF THE INVENTION 1. The invention proposes, for use in areflection scanner for detecting surface defects in a photographic web,that the light which is used be polarized, and be so beamed at a grazingangle with respect to the web that the plane of polarization of suchlight is perpendicular to the plane of incidence for the light. Such apractice prevents the beamed radiation from penetrating through theemulsion (the surface of which is to be examined) for reflection off,and absorption by, the base support for the emulsion.

2. The invention further proposes that the polarized light which isbeamed as described above, preferably,

, be visible light.

The advantages to be gained by item (1) above are:

The light intensity level which is employed for reflec-.

tion scanning of a photosensitive material may either be reduced or, ifretained without modification, the signal-to-noise ratio seen by thephotopickup of the system will be greatly increased; in one embodimentof the invention, the signal-to-noise ratio was increased by a factor ofabout 20 times. Also, since substantially none of the beamed light isreflected from the base support for the emulsion, the problem ofambiguity is, attendantly, avoided.

The advantage to be gained from item (2) above, aside from thoseindicated above in connection with the Description Relative to the PriorArt, is that assurance can be provided that reciprocity law failure, asdesired, will obtain for reflection scanning of photographic websaccording to the teachings of U.S. Pat. No. 3,556,664: That is, sincepractically none of the beamed polarized visible light penetrates thecoated emulsion, concern for assuring reciprocity law failure inconnection with the scanning beam is greatly minimized.

The advantages which are gained by practicing the invention are directlyrelated to the specularity of the photographic film being inspected.

An object of the invention is to increase the efficiency of a reflectionscanner for detecting surface defects in the emulsion coated on aphotographic web.

Another object of the invention is to increase the reliability of areflection scanner for detecting surface defects in the emulsion coatedon a photographic web.

Another object of the invention is to facilitate the use of visiblelight in a reflection scanner for detecting surface defects in theemulsion coated on a photographic web, whereby easy system alignment,smaller spot size, and unambiguous signal detection will obtain.

The invention will be described with reference to the Figures, wherein:

FIG. 1 is a schematic diagram illustrating an embodiment of theinvention, and

FIGS. 2 and 3 are diagrams useful for explaining the advantages gainedby means of the invention.

Reference should now be had to FIG. 1, which shows a specularphotographic web 10 being passed over a roller 12. A laser 14, having acoherent polarized visible output, directs its output radiation via apolarity rotator 16 to focusing optics l8; and thence via a rotarymultifaceted mirror 20 (which, according to the teaching of U.S. Pat.No. 3,556,664, rapidly sweeps such radiation widthwise across the web10) to an inspection point(s) P on the web. Lasers for producingcoherent polarized visible light are now well known; and polarityrotators are also well known (e.g., the Model 310 P0- larization Rotatoremploying a half-wave retardation plate manufactured by Spectra-Physics,1250 West Middlefield Road, Mountain View, Calif. 94040).

The focused light which impinges upon point P of the web 10 is adaptedto graze off the web to a collecting mirror 22; and thence be focused bya mirror 24 to a photopickup 26 that is responsive to radiation producedby the laser 14. The photopickup 26 is cooperative with a using circuitor device 28 that registers changes (i.e., surface defects) in theoutput of the photopickup 26.

For sake of explanation, the laser 14 of FIG. 1, according to acceptednotation for indicating planes of polarization, is shown providingpolarized visible light having a plane of polarization that is in theplane of incidence for light beamed at point P of the web 10. Afterpassing through the polarity rotator 16, however, the plane ofpolarization for the laser light is rotated so as to be perpendicular tothe plane of incidence for the light beamed at web point P.

FIG. 2 indicates the effect of beaming, at a photographic element, lightthat is (largely) polarized in the plane of incidence. To be noted isthat part B of the original beam B is reflected off the surface of theemulsion, as desired; another part B of the original beam B is reflectedoff the base support for the emulsion; and.

part B,, is transmitted through and/or absorbed by the base support. Thepart B,, of the radiation not received by the photographic element iscompletely wasted; and, worse than that, the part B of the radiation,which is reflected from the face of the support base, creates theaforementioned ambiguity, since such radiation B may trigger thephotopickup 26 wrongly to indicate a surface defect in the emulsion.

Reference should now be had to FIG. 3 which depicts the polarizedradiation that is beamed at a photographic element as being polarizedperpendicularly to the plane of incidence. So long as the incidentradiation B sees a smooth specular surface, the radiation E is almostfully reflected B from the emulsion coat, with only a very small amountB 8 ever reaching and being reflected off the support base. Thus, energyis not wasted; and ambiguous signal outputs cannot be produced by thebase support.

Since very little light (B',,) in FIG. 3 ever enters the emulsion, useof polarized visible light for the beam B is facilitated becausereciprocity law failure will, in accordance with the teaching of U.S.Pat. No. 3,556,664, more assuredly obtain. And, as noted above, use ofvisi ble light in a reflection inspection system for photosensitivematerial means that system setup and alignment are more easilyimplemented; that a more sensitive visible light photopickup 26 may beemployed instead of a relatively hard-to-use infrared photopickup; andthat the size of the spot which is used to locate defects in the surfaceof the emulsion may be made extremely small for defect-resolutionpurposes.

[Consistent with the above-mentioned requirements for the reflectioninspection of photographic material by polarized light that has a planeof polarity perpendicular to its plane of incidence, for easypenetration of a photographic web during transmission inspectionthereof, as described in U.S. Pat. No. 3,556,664, the invention suggeststhat light having a polarization plane that is parallel to the incidentplane be employed] The invention has been described in detail withparticular reference to preferred embodiments thereof, but it will beunderstood that variations and modifications can be effected within thespirit and scope of the invention. For example, it would be within thescope of the invention to arrange the laser 14 (without a polarityrotator) so that the plane of polarization for its output energy isperpendicular to the indicated plane of incidence.

What is claimed is:

1. In a system for inspecting the specular surface of photosensitivematerial by means of radiation reflected off said surface, comprising:

a. means for providing and beaming electromagnetic radiation at agrazing angle with respect to the surface of said photosensitivematerial, and

b. signal producing photopickup means for receiving radiation thatgrazes off the surface of said photosensitive material, the improvementwherein said means for providing and beaming electromagnetic radiationis adapted to produce polarized electromagnetic radiation, and is sodisposed to beam said polarized electromagnetic radiation that the planeof polarization for said electromagnetic radiation is perpendicular tothe plane of incidence for said radiation as it grazes the surface ofsaid photosensitive material.

2. The invention of claim 1 wherein said means for providing and beamingelectromagnetic radiation is laser means.

3. The invention of claim 2 wherein said laser means comprises:

a. a laser of the type that produces polarized light,

and

b. a polarity rotator for receiving the laser light output and rotatingthe plane of polarity of said light output so that it is perpendicularto the plane of incidence for said radiation as it grazes the surface ofsaid photosensitive material.

4. The invention of claim 1 a. wherein said means for providingelectromagnetic radiation is adapted to provide visible light,

b. wherein the photopickup is responsive principally to visible light,and

c. wherein said system includes means for sweeping said visible lightacross the surface of said photosensitive material at a rate which issufficient to prevent latent images from being formed in saidphotosensitive material.

5. The invention of claim 4 wherein said means for providing and beamingvisible light is laser means.

6. The invention of claim 5 wherein said laser means comprises:

a. a laser of the type that produces polarized visible light, and

b. a polarity rotator for receiving the visible light output of saidlaser and rotating the plane of polarity of said visible light output sothat it is perpendicular to the plane of incidence for said light as itgrazes the surface of said photosensitive material.

1. In a system for inspecting the specular surface of photosensitivematerial by means of radiation reflected off said surface, comprising:a. means for providing and beaming electromagnetic radiation at agrazing angle with respect to the surface of said photosensitivematerial, and b. signal producing photopickup means for receivingradiation that grazes off the surface of said photosensitive material,the improvement wherein said means for providing and beamingelectromagnetic radiation is adapted to produce polarizedelectromagnetic radiation, and is so disposed to beam said polarizedelectromagnetic radiation that the plane of polarization for saidelectromagnetic radiation is perpendicular to the plane of incidence forsaid radiation as it grazes the surface of said photosensitive material.2. The invention of claim 1 wherein said means for providing and beamingelectromagnetic radiation is laser means.
 3. The invention of claim 2wherein said laser means comprises: a. a laser of the type that producespolarized light, and b. a polarity rotator for receiving the laser lightoutput and rotating the plane of polarity of said light output so thatit is perpendicular to the plane of incidence for said radiation as itgrazes the surface of said photosensitive material.
 4. The invention ofclaim 1 a. wherein said means for providing electromagnetic radiation isadapted to provide visible light, b. wherein the photopickup isresponsive principally to visible light, and c. wherein said systemincludes means for sweeping said visible light across the surface ofsaid photosensitive material at a rate which is sufficient to preventlatent images from being formed in said photosensitive material.
 5. Theinvention of claim 4 Wherein said means for providing and beamingvisible light is laser means.
 6. The invention of claim 5 wherein saidlaser means comprises: a. a laser of the type that produces polarizedvisible light, and b. a polarity rotator for receiving the visible lightoutput of said laser and rotating the plane of polarity of said visiblelight output so that it is perpendicular to the plane of incidence forsaid light as it grazes the surface of said photosensitive material.